1. Field of the Invention
The present invention relates, in general, to hermetic compressors and, more particularly, to a hermetic reciprocating compressor which uses a radial bearing capable of smoothly operating the parts of the compressor.
2. Description of the Related Art
Generally, compressors are machines that compress a substance, such as a gas refrigerant, to reduce a volume of the substance or change a phase of the substance. As an example of the compressors, hermetic reciprocating compressors, which are housed in hermetic casings and in which a rotation of a shaft is converted into a rectilinear reciprocation of a piston within a compression chamber, are typically used in refrigeration systems to compress a gas refrigerant, prior to discharging the compressed refrigerant to a condenser.
In conventional hermetic reciprocating compressors, the hermetic casing is fabricated with upper and lower casing parts assembled into a single body. A compression unit to compress the inlet gas refrigerant, and a drive unit to generate a drive power for the compression unit are installed in the hermetic casing.
In the conventional hermetic reciprocating compressors, the compression unit has a cylinder block, which is integrally formed in a frame and defines a compression chamber therein. A cylinder head is mounted to the cylinder block. The cylinder head has both a suction chamber to guide the gas refrigerant into the compression chamber, and an exhaust chamber to guide the compressed refrigerant from the compression chamber to an outside of the hermetic casing. A piston is received in the compression chamber to perform a rectilinear reciprocation in the compression chamber.
The drive unit is provided at a position under the compression unit, and includes a stator along which an electromagnetic field is generated when electricity is supplied to the stator. The drive unit also has a rotor, which rotates by the electromagnetic field generated along the stator, and a rotating shaft axially and securely penetrating a center of the rotor to rotate along with the rotor.
The rotating shaft axially passes a shaft bore formed in the frame, and an eccentric part having an eccentric shaft is provided at an upper portion of the rotating shaft. A thrust bearing is installed at a junction between the eccentric part of the rotating shaft and the frame so as to sustain axial loads, which act in the rotating shaft due to the weight of the rotating shaft.
A lower oil path is formed in a lower section of the rotating shaft, such that the lower oil path extends from a lower end to an intermediate portion of the rotating shaft. In such a case, an upper end of the lower oil path reaches a position level with a lower end of the frame. That is, the upper end of the lower oil path is terminated at a position corresponding to a lower end of a contact surface of the rotating shaft relative to the frame. A spiral oil groove is formed around a part of an outer surface of the rotating shaft such that the spiral oil groove is connected at a lower end thereof to the upper end of the lower oil path and is connected at an upper end thereof to an upper oil path formed in the eccentric part of the rotating shaft. Therefore, when the rotating shaft rotates, oil is drawn upward from a bottom of the hermetic casing while orderly flowing through the lower oil path, the spiral oil groove, and the upper oil path. The contact surfaces of the rotating shaft relative to the frame and the thrust bearing are lubricated. That is, an oil layer is formed on each of the contact surfaces of the rotating shaft relative to the frame and the thrust bearing, so that the rotating shaft rotates smoothly.
However, the conventional hermetic reciprocating compressors are problematic as follows. That is, since the thrust bearing sustains only axial loads acting in the rotating shaft due to the weight of the rotating shaft, the rotating shaft is held with friction within the shaft bore of the frame.
Since the rotating shaft is held with friction within the shaft bore as described above, the rotating shaft may undesirably move in the shaft bore. In such a case, severe friction occurs at the junction between the rotating shaft and the shaft bore of the frame. The conventional hermetic reciprocating compressors thus easily generate noise to upset those around the compressors. The frictional contact of the rotating shaft with the shaft bore of the frame also undesirably reduces compression efficiency of the compressors.
In addition, the spiral oil groove must be formed around the outer surface of the rotating shaft in an effort to lubricate the junction between the rotating shaft and the shaft bore of the frame to avoid frictional contact of the rotating shaft with the shaft bore. However, the machining of the spiral oil groove around the rotating shaft complicates a production process of the compressors. Furthermore, it is difficult to machine the spiral oil groove around the outer surface of the rotating shaft.
The cylinder block integrally formed in the frame and the shaft bore of the frame must be arranged such that the cylinder block is always perpendicular to the shaft bore. However, the conventional hermetic reciprocating compressors may not always form the desired perpendicular arrangement of the shaft bore relative to the cylinder block, due to a mechanical tolerance of the frame. In such a case, severe friction occurs at the junction between the rotating shaft and the shaft bore to cause excessive wear on the rotating shaft and the shaft bore, in addition to generating noise.